In the automobile industry, machinery industry, and the like, there has been an increased demand for sensors capable of precisely detecting acceleration or angular velocity of a moving object (body). In general, an object which carries out free movement in a three-dimensional space bears an acceleration in an arbitrary direction and an angular velocity in an arbitrary rotational direction. For this reason, in order to precisely grasp movement of this object, it is necessary to independently detect acceleration components in every respective coordinate axial direction and angular velocity components about every respective coordinate axis in the XYZ three-dimensional coordinate system, respectively.
Hitherto, multi-dimensional acceleration sensors of various types have been proposed. For example, in the International Laid Open No. WO88/08522 based on the Patent Cooperation Treaty (U.S. Pat. No. 4,967,605/U.S. Pat. No. 5,182,515), there is disclosed an acceleration sensor in which resistance elements formed on a semiconductor substrate are used to detect applied acceleration components in every respective coordinate axial direction. Further, in the International Laid Open No. WO91/10118 based on the Patent Cooperation Treaty (U.S. patent application Ser. No. 07/761,771), a multi-axial acceleration sensor having self-diagnostic function is disclosed. Further, in the International Laid Open No. WO92/17759 based on the Patent Cooperation Treaty (U.S. patent application Ser. No. 07/952,753), there is disclosed an acceleration sensor in which electrostatic capacitance elements or piezoelectric elements are used to detect applied acceleration components in every respective coordinate axial direction. Further, also in the Japanese Patent Application No. 274299/1990 (Tokuganhei 2-274299) specification and the Japanese Patent Application No. 416188/1990 (Tokuganhei 2-416188) specification (U.S. patent application Ser. No. 07/764,159), a multi-axial acceleration sensor similar to the above is disclosed. In the Japanese Patent Application No. 306587/1991 (Tokuganhei 3-306587) specification (U.S. patent application Ser. No. 07/960,545), a novel electrode arrangement in a similar multi-axial acceleration sensor is disclosed. In addition, in the International Application PCT/JP92/00882 specification based on the Patent Cooperation Treaty, a multi-axial acceleration sensor using piezoelectric element of another type is disclosed. The feature of these acceleration sensors is that a plurality of resistance elements, electrostatic capacitance elements or piezoelectric elements are arranged at predetermined positions of a substrate having flexibility to detect applied acceleration components on the basis of changes in resistance values of the resistance elements, changes in capacitance values of the electrostatic capacitance elements or changes in voltages produced in the piezoelectric elements. A weight body is attached on the substrate having flexibility. When an acceleration is applied, a force is applied to the weight body and bending occurs in the flexible substrate. By detecting this bending on the basis of the above-described changes in resistance values, capacitance values or charges produced, it is possible to determine acceleration components in respective axial directions.
On the contrary, the inventor of this application cannot find any literature relating to a multi-dimensional angular velocity sensor so far as he knows. Ordinarily, angular velocity sensors are utilized for detecting an angular velocity of a power shaft, etc. of a vehicle, and only have a function to detect an angular velocity about a specific single axis. In such cases of determining a rotational velocity of the power shaft, it is sufficient to use an one-dimensional angular velocity sensor. However, in order to detect angular velocity with respect to an object which carries out free movement in a three-dimensional space, it is necessary to independently detect angular velocity components about respective axes of the X-axis, the Y-axis and the Z-axis in the XYZ three-dimensional coordinate system. In order to detect angular velocity components about respective axes of the X-axis, the Y-axis and the Z-axis by using one-dimensional angular velocity sensors conventionally utilized, it is necessary that three sets of angular velocity sensors are prepared to attach them in specific directions permitting detection of angular velocity components about respective axes. For this reason, the structure as the entirety of the sensor becomes complicated, and the cost also becomes high.